Researchers found proof that mining disrupted the natural evolution of the distribution of chemical elements in the Zhaotong-Bijie-Yibin-Leshan-Luzhou area.
Recent studies have found that arable land in Southwest China contains unusually high (and potentially harmful) levels of heavy metals. Mining activity in the area was thought to be the reason. However, understanding the processes underlying the distribution of chemical elements in soils is complicated, and so is finding evidence pointing to human activity being the culprit of changes in this distribution.
In a new study published in Earth Science Frontiers, a research team from the Chinese Academy of Geological Sciences and China Geological Survey, led by Dr. Hangxin Cheng, performed a comprehensive chemical analysis of a particular mountainous region in Southwest China. This region, referred to by the researchers as the Zhaotong-Bijie-Yibin-Leshan-Luzhou area, is composed mainly of mountains and valleys, and covered mostly by forests and farmlands.
Most importantly, this region has seen intense mining activity for lead, zinc and silver over centuries. "Research in this area can reveal the driving mechanisms behind changes in the content and macroscopic distribution of elements in soil, thereby providing scientific solutions for the rational exploitation and utilization of natural resources," explained Cheng.
About 100 researchers and workers gathered more than 112,000 top- and deep-soil samples throughout the region and analysed their chemical composition and acidity. The analysis was performed based on the "epigenetic geochemical dynamics" theory, which encompasses modern human understanding of what causes changes in the composition of surface rocks after their formation. The processes and factors considered in this theory range from naturally occurring chemical reactions involving metallic ions to the solubility in water of various substances, as well as geological dynamics and the effects of weather, elevation and human activities.
The researchers highlighted four main findings that collectively provide an explanation for the observed distribution and state of chemical elements in the surveyed area. First, the parent material, which is the geological material on top of which soil forms and accumulates, largely dictates the distribution and state of chemical elements found in land resources. Second, epigenetic geochemical dynamic processes reshape the distribution patterns of these elements in the topmost layers of soil. Third, biogeochemical processes, which mostly involve organic material and its incorporation and distribution by living organisms, are responsible for driving the evolution of land quality. Finally (and as initially expected), strong human activities like mining disrupt the natural evolution of the distribution of chemical elements.
This study gives researchers a better understanding of how the various dynamic processes in one particular region on the Earth's surface determine its distribution of chemical elements, which quite literally act as a base (soil) for the local ecosystems. "Further studies should be conducted to analyse a variety of landscapes, including forests and swampy landscapes, low mountains, and alpine lakes, to represent considerable advances in epigenetic geochemical dynamics and help us establish a foundation for the development of scientific theories of Earth's systems," states Cheng. The results of this study could provide a scientific foundation for designing rational land-use management strategies, as well as food safety and health protection measures in Southwest China.